Patent GB-417189-A (GB)
Abstract: 417,189. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. March 30, 1933, No. 9662. Convention date, April 1, 1932. [Class 40 (iv).] Reverting impulses and other signals are passed over a junction FL in the form of alternating current with the aid of repeaters BR1, BR2. The invention is described with reference to a system in which the switches at both offices are of the kind described in Specification 180,994, [Class 40 (iv)], and send impulses only in the odd positions to counters which take a step at the beginning and end of each impulse. Control of switches. When the setting of the outgoing selector GV1 has been completed, RR1 in the register-controller connects battery to the a-wire energizing R1 which is followed by R2, R3, R4, R5. R3 locks and releases R1 which is followed by R2. An impulse of A.C. is thus sent by R1 over the junction to R20 which energizes R21 which locks up. At the end of the impulse, R20 falls and energizes the clutch magnet GVM over R23 which is followed by R24, R25. R24 connects a source of A.C. to the junction to energize R7 which energizes the impulse relay RR2 in the register-controller and removes a short circuit from R6. The reverting impulses from the switch are repeated by R27 which releases R25 to interrupt the A.C. circuit over the junction and so releases R7 and RR2. It will be seen that the register is kept by this means one step ahead of the switch. When it reaches the marked position, RR1 releases R3 which disconnects R7 from the junction and releases R5. The A.C. circuit over the junction includes a bridge rectifier L1 to which is connected one winding of a differential relay R26, the other winding of which receives equal impulses from a local A.C. circuit including a resistance r6, which is adjusted in accordance with the junction impedance, and a rectifier L2. When R7 is disconnected the impedance of the junction circuit rises and if the switch is in an even position and R27 therefore is not energized the current through the upper winding of R26 is reduced, that through the lower winding being increased owing to the reduction in the voltage drop in common resistances r4, r5. R26 therefore pulls up and R27 disconnects the clutch magnet when the switch moves to its next (odd) position. If R7 is disconnected with the switch in an odd position (R27 energized) R26 pulls up and disconnects the clutch magnet when R27 is released by movement of the switch to the next (even) position. R28 holds the clutch magnet circuit open long enough for R23 to fall back and energize R29 which locks up, switches through, and releases R24. When R20 receives the starting impulse for the next switch, R29 is unlocked and a circuit is made over the a-wiper for its clutch magnet (GVM being disconnected locally by means not shown). Release of faulty junction. If R6 is not enabled to pull up, by the response of R7 to the first A.C. impulse, before the relapse of R2, the test relay PR in the switch GV1 is shunted out and the switch moves on. Reply and clearing signals. When the called party replies, feed relays R30, R31 pull up, followed by R24 and by R32 which locks and cuts off R24. An A.C. impulse is thus sent back to R7 which is followed by R8, R9, which remain locked up, R9 connecting an inductive bridge 15 across the calling side of the repeater to repeat the signal. When the called party hangs up, R30, R31 and R32 fall back making a temporary circuit for R24 which sends an A.C. impulse to R7 which releases R8. At the end of the impulse R9 falls and disconnects the inductive bridge 15. When the calling party hangs up, R4 releases R6 and a temporary circuit is made for R10 which is very sluggish and causes R1 to send an A.C. impulse forward. R20 in response to this signal unlocks R29 and shunts out R21 and at the end of the signal R22 falls back. The Specification as open to inspection under Sect. 91 states that the invention can be employed in a system in which the setting of the registers of a forward-impulsing register-controller is controlled by a revertive-control office. This subject-matter does not appear in the Specification as accepted.